#include<iostream>
#include<cmath>
#include<iomanip>

int main()
{
	
	double a, b, c;
	cout << "cin a,b,c:";
	cin >> a >> b >> c;
	if (a + b > c&&b + c > a&&c + a > b)
	{
		double s, area;
		s = (a + b + c) / 2;
		area = sqrt(s*(s - a)*(s - b)*(s - c));
		cout << setiosflags(ios::fixed) << setprecision(4);
		cout << "area=" << area << endl;


	}
	else cout << "Error";

	return 0;
}

